#include <cstdio>
using namespace std;

int main()
{
    int n = 0, n_1 = 1, n_2 = 1;
    double sum = 0;
    for (int i = 0; i < 20; i++) {
        n_2 = n_1;
        if (n != 0)
            n_1 = n;
        n = n_1 + n_2;
        sum += (double)n / (double)n_1;
    }
    printf("%.6f\n", sum);
    return 0;
}